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THz Activities


In addition to the activities in the mid infrared (MIR) the group is also using synchrotron radiation (SR) in the THz range (spectral interval between 100 µm to 8000 µm) for spectroscopy. The electron storage ring may be operated in a special mode denoted as low-a optic for providing high radiation intensity in this spectral range. The MLS is the first electron storage ring worldwide designed and prepared for low-α operation mode based on the octupole correction scheme, for the production of CSR in the far-IR and THz region [1]. The reduction of the electron bunch length to the level of the emitted THz radiation wavelength provides a coherent emission of synchrotron radiation above a wavelength of 200 µm. This special operation mode increases the radiant power by 5 orders of magnitude compared to the conventional operation mode, as shown in Fig. 1. The special storage ring optic leads not only a gain in power (maximum measured integral power was 60 mW) but also a shortening of the emitted pulse length below 10 ps (FWHM). Recent measurements proofed the MLS to be a highly stable and reproducible THz source.


  • source for time resolved measurements down to ps range with repetition rates up to 500 MHz [6, 7]
  • THz Power measurement capabilities up to 60 mW integral power [3]
  • spectrally resolved measurements down to 14 mm wavelength (0.7 cm­-1) [1]
  • spectral resolution down to 0.07 cm-1

Technical Specifications

  • FTIR spectrometer Vertex80v with Mylar beam splitters: 125 μm, 50 μm, 23 μm, 6 μm
  • Transmission/ reflection cryostat (2.4 K – 500 K) (Oxford Optistat CF)
  • various detectors to cover the complete spectral range including: Indium Antimonide (InSb) hot electron bolometer, Germanium bolometer, Silicon bolometer (4 K and 1.7 K), room temperature (RT) DTGS, Thomas Keating absolute THz powermeter (RT)
  • Hamamatsu streak camera for pulse length measurements (in UV and VIS)
  • various polarizers, filters & focusing mirrors

Research Topics

The group is involved in the characterization of detectors for the THz range with regard to time response, using either the possible 6.25 MHz repetition rate of the electrons revolution frequency or the 500 MHz repetition rate resulting from the radiofrequency device of the storage ring. Using the MLS as a high power THz source the group also aims at supporting the development of novel materials in the field of spintronics. Ongoing specific research activities are:

  • Pump–probe measurements for detector characterization (collaboration with DLR)
  • Characterization of novel materials for spin-based electronics [4] (collaboration with Hitachi Cambridge Laboratory)
  • Storage ring diagnostics regarding the stability, spectral and time resolved emission characteristics (variation of bunch length, ring current, filling pattern)
Fig. 1: Emitted spectral power and gain of the coherent synchrotron radiation (CSR) at the optimized THz beamline at the storage ring MLS compared to the conventional SR from a dipol [1].


  1. MLS - The first electron storage ring optimized for generating coherent THz radiation, PRST-AB 11, 030705 (2008)
  2. Opens external link in new windowJ. Feikes et al. Phys. Rev. STAB (2011), 14, 030705
  3. R. Müller et al., J Infrared Milli Terahz Waves 32, 742 (2011).
  4. J. Wunderlich et al., Phys. Rev. Lett. 94, 47204 (2005).
  5. J. Feikes et al., IGFA BD Newsletter 57, (2012)
  6. P. Probst et al., Appl. Phys. Lett. 98, 043504 (2011).
  7. P. Probst et al., Phys. Rev. B 85, 174511 (2012).
  8. A quarter-century of metrology using synchrotron radiation by PTB in Berlin, Phys. Status Solidi B 246, 1415 (2009)
  9. Absolute Measurement of the MLS Storage Ring Parameters, PRST-AB 11, 110701 (2008)